Study On The Methodology Of Diagnosis For Transformer Inter-turn Short Circuit Based On Wavelet Analysis

Distribution transtormer is an important device in the power supply system, once its failure can cause power outages. According to statistics, a great number of the transformer accident was caused by a short circuit between the transformer turns. Based on the large number of experimental data analysis and processing, a new inter-turn short circuit transformer diagnostic methods is proposed. In this paper, the ground current of transformer core as the signal source, Using wavelet multi-resolution technology the signal wavelet multiscale decomposition, the decomposition of different signals of the same scale, get the high frequency components of the signal, achieve short-circuit fault diagnosis between transformer winding turns by comparing the number of the high-frequency component contained in different signals in the decomposition of the same scale. To illustrate the effectiveness of the method, the paper through a series of experiments and data processing, verify the effectiveness and feasibility of the method.Based on the method of calculating short circuit reactance in transformer design, a study on effects of internal short circuit faults on the short circuit reactance has been carried out. The results show that the internal short circuit causes the unbalanced axial distribution of ampere-turns and increase the transverse leakage magnetic field (TLMF) component. The existence of TLMF will increase the leakage inductance. However, when the internal shirt circuit happens in the primary winding, the contribution of decreasing leakage inductance owing to decrease of the total ampere-turns is more considerable than the contribution of increasing leakage inductance owing to increase of TLMF and hence, the short circuit reactance decreases. When the internal shirt circuit happens in the secondary winding whose terminals are connected together, the short circuit reactance at primary side may increases. No matter where the short circuit happens, the reactance is not equal to rating one and its value increases or decreases nonlinearly with the change of the fault position.